Traffic signal technology is a key element to a well-designed traffic signal system and crucial to improving safety on Minnesota roads.
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Intersection Control Evaluation
Guidelines for Implementation
The goal of Intersection Control Evaluation (PDF) is to select the optimal control for an intersection based on an objective analysis. These guidelines provide direction and recommendations for completing an Intersection Control Evaluation.
The most important factors to complete the study are:
Project origination. The project does not have to be under MnDOT jurisdiction. If the project is not a MnDOT project the originator is responsible for completing the Intersection Control Evaluation. The MnDOT Traffic Engineer is accountable for review and approval so they must be involved early in the process (unless an outside consultant is hired for this purpose).
Size/Type of Project. A memo/letter must be submitted for approval stating why the work needs to be done and why other types of traffic control are not being considered. Smaller projects require less analysis. Signal rebuilds will require minimal analysis.
The amount of analysis will depend on each project’s location and scope. Intersections which are part of larger projects and/or have significant impact to adjacent intersections will require significant analysis and documentation. Stand-alone intersections will require a safety and capacity analyses and documentation of other factors such as cost and Right of Way information.
Traffic control decisions made earlier in the project will improve the quality of the final design and minimize conflicts.
The process is described in Tech Memo 07-02-T-01 (PDF).
General. The purpose of Intersection Control Evaluation is to determine the optimum traffic control based on a technical and financial analysis as well as political factors. The following is general guidance on completing an ICE study.
- Avoid overanalyzing a location. If a decision has been made or one traffic control type will be the choice, document the decision making process and include in a short memo or basic report. It still may be necessary to gather traffic data, conduct a warrant analysis and complete a safety and capacity analysis.
- A decision may be reached after Phase 1. It will still be necessary to develop preliminary layouts, cost estimates and other project development tasks, but an Intersection Control Evaluation report can be completed at this time. However, if the project development process negates what has occurred in Phase 1, it will be necessary to revise the report.
- All projects programmed for fiscal year 2008 and beyond must have an Intersection Control Evaluation completed.
- For larger projects in areas where traffic volumes may increase on the local system as well as the arterial, careful consideration should be taken to determine if an Intersection Control Evaluation is necessary. Relying on future traffic projections, in which traffic volume warrants are barely met, should not be a requirement to perform an Intersection Control Evaluation. Generally speaking, if warrants are unlikely to be met within a 5 year time frame, an Intersection Control Evaluation is unnecessary.
Warrant Analysis. For any intersection beyond thru-stop control, a warrant analysis must be completed.
- Traffic volumes must be obtained. For most cases existing volumes are preferred. However, future anticipated volumes may be used if development is imminent. For new roadways projections must be used.
- Confer with the District Traffic Engineer on which warrant will be allowed. In most instances, follow the procedures within the Tech Memo.
Safety Analysis. If the warrant analysis confirms that additional traffic control will be needed at a location, a safety analysis should be performed for all intersection alternatives.
- Existing crash records should be obtained and shown in the report as stated in the Tech Memo.
- For each alternative an estimate of future crashes should be obtained. It is suggested that this analysis utilize crash rates to keep it simple. If desired, a more thorough crash reduction methodology can be used. A table of average crash rates (XLS) for each alternative has been developed and will be updated and revised periodically. A comparison of anticipated total crashes and severe crashes should be documented for a target year.
- Although stated in the Tech Memo, it is unnecessary to compute crash reductions per year and crash cost. Currently, this additional data is considered to be unnecessary.
Capacity Analysis. For comparison purposes a capacity analysis should be conducted for each alternative. We recognize that the capacity analysis contained in current software for roundabouts has some issues. We anticipate advances in this area and may change software requirements at a future date.
- Year of analysis. 20 year projects are the default for this type of analysis, however, due to the variability in accuracy of traffic projections, shorter time frames should be strongly considered in many instances. If total development is expected to occur within 5 years, 5 years should be the target year for analysis. If the capacity analysis appears to highlight near failures within this timeframe, future projections should be analyzed.
- Choice of models. Generally speaking, avoiding the use of VISSIM should always be the rule. If analysis of individual intersections indicates no potential for queues impacting adjacent intersections, there is no need to conduct a VISSIM analysis, no matter how many intersections are analyzed or their lack of adequate spacing. However, if the opposite is true, first optimize the individual intersection analysis or increase geometric options which increase capacity and only if that fails should VISSIM be used.
- The primary goal of this exercise is to first – insure that each intersection will operate acceptably for each type of traffic control and second – to provide a gross level of comparison between options.